The present invention relates to a rotation angle sensor for use in control of fuel injection and ignition timing of an internal combustion engine.
Recently, internal combustion engines are provided with electronic units for controlling fuel injection and ignition timing. This type electronic unit includes a rotation angle sensor which detects a crank position of the internal combustion engine, for determining fuel injection and ignition timing of the internal combustion engine on the basis of the information.
A typical rotation angle sensor has a rotating member adapted to rotate in synchronism with an internal combustion engine, and a stationary pickup opposing to the rotating member, and is so formed as to detect a crank angle of the internal combustion engine through changes of magnetic flux caused on the pickup upon rotation of the rotating member. Such a rotation angle sensor is disclosed in, for example, Japanese Patent Unexamined Publication No. 60 -174048, which corresponds to U.S. Pat. No. 4,628,891, and Japanese Patent Unexamined Publication No. 3-12501 which corresponds to U.S. Pat. No.5,027,067.
Conventionally, a rotation angle sensor is attached to a crankshaft or cam shaft of an internal combustion engine to detect rotation of the shaft. The rotation angle sensor is rather preferably attached to the cam shaft, because the cam shaft is usually provided at a top of the internal combustion engine and easy access for assembly or service is ensured. In most of internal combustion engines, however, a cam shaft and a crankshaft are coupled to each other by a timing belt or chain. For this reason, the cam shaft is deviated in phase with respect to the crankshaft within the range of manufacture accuracy of a coupling drive member. As a result, due to such a deviation of phase of the cam shaft with respect to the crankshaft, the rotation angle sensor attached to the cam shaft cannot always detect the crank position accurately, which causes an error in initial setting of the ignition timing.
With a view of compensating for such an error in initial setting of the ignition timing, for example, Japanese Utility Model Unexamined Publication No. 63-48110 discloses a mechanical ignition timing adjusting mechanism and Japanese Patent Unexamined Publication No. 59-134377 discloses an electrical ignition timing adjusting mechanism. However, any of the disclosed mechanisms is complicated in structure and requires a relatively expensive production cost.